Zipper Merge -- A Literature Review

It's getting common to see transportation departments1, 2, 3, 4 and news stories5, 6, 7 advocating zipper merge (AKA late merge), claiming that it is safer and allows higher throughput. As someone who naturally doubts the pronouncements of transportation departments, I thought I'd look into the research behind it.

First of all, what is zipper merge? It's the idea that when lanes merge, the traffic should cluster up at the merge point, where cars will take turns merging. Some variants include active signage to signal which car should go next, but mostly not. This is compared to "early merge", where people start to get over as possible as soon as possible.

Outside of some specific situations (2 lanes going down to 1 where neither lane is obviously the one going away) this has never made much sense to me. Humans overbrake, amplifying any slowdown. Encouraging gradual merging over a long distance, where cars can slow down enough to let others in just by coasting, seems obviously better. And calmer, and more polite. Also, to be fair, the kind of people who are really vocal about zipper merge tend to put me off. But I know better than to trust my gut reaction on such things -- that's what we have science for! So what does the science say?

Under various names, late merge has shown up in papers as early as 199015. The idea really started to take off after some work in the Netherlands in the late 90s.13 Of the later work, two things really stand out to me. First, they almost all are only talking about 2 lanes merging down to 18, 9, 10, 16. Also, many of the papers8, 15, 16, 17, 18 are primarily reporting on simulated results or are lit reviews12, 14 like this post.

The number of lanes in question seems key to me. In the situation of just 2 lanes going down to 1, zipper merge certainly makes a lot more sense. The problem here is that these results are over-generalized to apply to any merging scenario. The entrance to the express lanes on N I-5 in downtown Seattle is a prime example of this. There, a lane becomes exit-only that many people want to take. Many of them apply late merge techniques, zooming up to the front of the line and then trying to merge. In doing so, they block an entire lane that would otherwise be open, and this sometimes carries over to slowing down even the next lane, as people dodge out around the blockage. This is the core of my objection to zipper merge -- it encourages people to be jerks.

The simulation issue is also critical. The simulations are all calibrated using real world data, but that mostly extends just to things like measuring the average time it takes to change lanes. The distinction between real world measurements and simulated results are often lost in later citations, such as in the heavily cited McCoy 200114 paper. It states that "Early Merge has been found to increase travel times", while only referencing two simulation studies15, 16 -- and the second citation only provides parameters for simulating a late merge system that hadn't been implemented yet at the time of publication!

Overall, the results seem pretty muddy to me. Of the others, one9 lacked a control and another10 had neutral results. There are several papers that do find pro-zipper11, 17, 18 results, but those are qualified as being tied to specific traffic volumes and/or the presence of active signage. This is a hard problem to investigate, since it involves changing habits of a large number of people. It shouldn't be surprising if the results are inconclusive.

Does any of this matter? I think so. Look at the news articles promoting zipper merge -- "science says to stop being polite" is a common theme. We should always be extra dubious when evidence seems to justify us doing what we wanted to do in the first place.

1: Minnesota DOT

2: Kansas City DOT

3: Nebraska DOT

4: Missouri DOT

5: Why Last-Second Lane Mergers Are Good for Traffic, New York Times, October 12, 2016

6: All hail the zipper merge: How Canadian politeness is killing the efficiency of our highways, National Post, January 23, 2017

7: Have you ever heard of the zipper merge technique?, Houston Chronicle, July 25, 2016

8: Wakita, Y., et al. "Comparison of zipper and non-zipper merging patterns near merging point of roads." Nature-Inspired Computing Design, Development, and Applications. IGI Global, 2012. 221-231. OPEN ACCESS

9: Grillo, Lia, Tapan Datta, and Catherine Hartner. "Dynamic late lane merge system at freeway construction work zones." Transportation Research Record: Journal of the Transportation Research Board 2055 (2008): 3-10. PAYWALL

10: Idewu, Wakeel, and Brian Wolshon. "Joint merge and its impact on merging speeds in lane reduction areas of construction zone." Transportation Research Record: Journal of the Transportation Research Board 2169 (2010): 31-39. PAYWALL

11: Kurker, Michael, et al. Minimizing User Delay and Crash Potential through Highway Work Zone Planning. No. FHWA/TX-13/0-6704-1. 2014. OPEN ACCESS

12: Walters, Carol H., et al. Understanding road rage: Summary of first-year project activities. No. TX-01/4945-1,. 2000. OPEN ACCESS

13: Dijker, Thomas, and Piet HL Bovy. "Influencing lane changing at lane drops." Transportation Research Board 1999 Annual Meeting CD-ROM. 1999. NOT AVAILABLE ONLINE

14: McCoy, Patrick, and Geza Pesti. "Dynamic late merge-control concept for work zones on rural interstate highways." Transportation Research Record: Journal of the Transportation Research Board 1745 (2001): 20-26. OPEN ACCESS

15: Mousa, Ragab M., Nagui M. Rouphail, and Farhard Azadivar. "Integrating microscopic simulation and optimization: Application to freeway work zone traffic control." Transportation Research Record 1254 (1990). PAYWALL

16: Tarko, Andrzej P., Sreenivasulu R. Kanipakapatnam, and Jason S. Wasson. "Modeling and Optimization of the Indiana Lane Merge Control System on Approaches to Freeway Work Zones, Part I." Joint Transportation Research Program (1998): 345. OPEN ACCESS

17: Ramadan, Ossama E., and Virginia P. Sisiopiku. "Evaluation of merge control strategies at interstate work zones under peak and off-peak traffic conditions." Journal of transportation technologies 6.03 (2016): 118. OPEN ACCESS

18: Kang, Kyeong-Pyo, Gang-Len Chang, and Jawad Paracha. "Dynamic late merge control at highway work zones: evaluations, observations, and suggestions." Transportation Research Record: Journal of the Transportation Research Board 1948 (2006): 86-95. OPEN ACCESS

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A creature of perfect morality

(This exploration was inspired by de Beauvoir's Ethics of Ambiguity, coincidentally reinforced by parts of Palmer's Seven Surrenders, plus some of the style of Kierkegaard's Fear and Trembling. So if it's a little pretentious, well, you now know why.)

How do we value human life?

I'm walking down the street. Two cars crash and burst into flames. I help the driver in the first car, as it is slightly closer to me. While I get the first driver to safety, two people in the other car burn to death.

When on the bus, I sometimes look at the other passengers and simply try to appreciate the human mind. They're a commonplace miracle, yes, but a miracle none the less. Each is a unique collection of experiences and thoughts, never repeated before or since. Each a completely distinct portal into this world. In a very real sense, each is its own universe. Trying to put a value on them is like putting a value on an entire library of lost works.

Human lives are the only thing that we know for certain adds meaning to the universe. How do you assign a value to that which creates value? It's literally priceless, yet we've never found a moral/political/economic system that doesn't demand constant appraisals. How much of the budget should be dedicated to eradicating a specific cancer? How slow are you willing to drive to keep all pedestrians safe?

I'm walking by some train tracks. An out-of-control trolley is rolling towards a switch in the track. On one side of the switch there is a person tied to the tracks. On the other side, there are 10 people. Without looking to see what position the switch is in, I pull out my phone and call 911, trying to save a few seconds of response time. In the background, screams.

It's tricky, working with infinity. The promise of a future paradise has lead to some of the worst atrocities in all of human history. It doesn't matter if it is of the heavenly or earthly kind, religious or secular, the danger of paradise is assigning an infinite value to begin with. No number of deaths, no horror or depravity conceivable can't be justified in the here and now if you believe it can lead to an infinite reward.

Even mathematically, it took us a long time to learn how to safely use the concept of infinity. Xeno's Paradox was a legitimate problem until infinite sums were conquered, a process which took 2000 years. We're pretty good at it now, calculating with the infinitely large and small, an achievement which has led to wonders. The modern world simply cannot happen without calculus.

On my left, a cruise ship is sinking. On my right, a rowboat. I flip a coin to decide which I should help.

It could be human lives are of infinite value, but we haven't developed the appropriate analytical tools yet. There could be a rigorous calculus of ethics out there, waiting to be invented.

Can we imagine what that would be like, living with a consistent moral system that really sees all lives as having unbounded value? I don't think it would be recognizably human. The creature you would have to become, who cannot see the difference between a single death and a million -- is it a saint, or a monster?

From my limited, mortal perspective, I think it's best to just keep pushing up the value of human life. Regular, monotonic, finite increments. Let it reach infinity when t itself does. That might be soon enough.

I'm performing CPR on an octogenarian. On the other side of the room, an ICBM launch starts counting down. I wonder if anyone else will arrive in time to deal with it.

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Personal space

About once a year, I'm struck by the urge to knit something. Sometimes this is triggered by a coworker having a baby.

I often knit on the bus when I'm working on a project. And that has lead me to an interesting observation: other men will sometimes give me far less personal space if I'm knitting.

The archetypal situation has me sitting in the back of the bus, my feet on up the seat in front of me. (I, of course, am ready to contract the space I'm using as the bus fills up, but I see no reason not to be comfortable until then.) Normally, when other men get on, they will naturally space themselves around the back seats, leaving large gaps between each other. Having another man sit next to me -- even counting seats in the row perpendicular to where I am -- is basically unheard of unless it's filling up and they have no choice. Yet when I'm knitting, and only when I'm knitting, I've had someone sit right there when the back of the bus only has 0-1 other people in it. This has happened enough times I lost exact count, maybe half a dozen now. It's very noticeable, because I have to jerk my feet back as they sit down. And then I look up, thinking I had been rudely unobservant and let the bus get more crowded than politely allows the feet-up position. But no, it's still super empty.

The thing is, I don't get an aggressive vibe from these dudes. They aren't trying to punish me for acting insufficiently masculine. (Trust me, it's been a few yearsdecades since high school, but I know what that looks like.) And they aren't then looking up, registering that I'm male, and looking disappointed/disgusted/whatever that I'm not a woman they wanted to hit on or anything. As far as I can see, I'm just not being seen as someone whose personal space needs any consideration. I don't think it's conscious, I just don't entirely register any more. They won't sit on me, quite, but other than that I have no claim on any personal space around me. They don't apologize for making me move my feet, they don't even pause when sitting down. I might as well be a potted plant. All because I'm engaged in a stereotypical female activity.

So that's interesting.

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As it does on a regular basis, the subject of gerrymandering has come up again. And, as always, I'm seeing people make the perfectly reasonable suggestion that we deal with it algorithmically. I'm all for that... until it is claimed that this would somehow make it non-political. And that's just bullshit. Dangerous bullshit.

The Gerry-Mander Edit.png

Districting is hard because it's very hard to define an obvious set of criteria by which to rate potential districts. We have some basic parameters set for the federal level: break each state into n districts, each containing roughly 700K people, and don't allow the districting to artificially limit the political power of racial minorities. Specifically, it wants to avoid "cracking" (breaking a group's voting power over many districts, so their votes are overwhelmed everywhere) or "packing" (lumping all their voting power into a small number of districts, giving them a few safe seats but still reducing their representation far under what it should be going by population).

The problem is, obviously, that these are very squishy guidelines. So can't we firm them up with some hard mathematical definitions, write up a segmentation algorithm, and let it do its absolutely objective magic? Sure! We just need to define some kind of scoring system to judge how good or bad a potential set of districts for a state is.

Here are some factors I can think of that such a system could use for its scoring:
* District shape -- the eponymous gerrymander was a point of satire because of how strung out it was. Keeping districts reasonably compact is usually a good thing.
* Geography -- we don't want a district that extends across a mountain range or other significant barrier, since the people on either side probably have little contact with each other and don't make sense as a single political unit.
* Road/train networks -- same as above.
* Racial composition
* Cultural composition
* Age composition
* Education level
* Religion
* Types of economic activity
* Economic ties to other parts of the country/world
* Climate
* Soil types
* Favorite NFL team
* Literally a billion other possible options

But which of these factors does that is best? In what ratios? I could certainly come up with a solution I like, but it wouldn't be perfect. There isn't a perfect solution to this problem. It's not the kind of problem where "correct" even has a meaning. Given a defined algorithm, math can give you a perfectly objective answer, but it can't choose the algorithm in the first place.

And that's where I find this talk gets really dangerous. It wants to pretend we live in a world with provably perfect solutions to messy human problems. If we just let some smart math/computer types work on it, they can fix everything, and save us from the dreaded specter of politics. But that would just be putting the imprimatur of unquestionable objectivity on yet another arbitrary decision. Governments based on that kind of thinking tend to get all great-leap-forwardy and mass-starvationy.

The real error in this thinking is that it assumes politics is a bad thing. It isn't. Being political isn't a bad thing. Politics just means the process by which we come to a decision when there are conflicting human desires. You have to accept that deciding on something as hopelessly complex as districting is, yes, going to be political. And that's okay!

Personally, my solution would be to set up a framework for an official, national algorithm, running against standardized data provided by the Census Bureau. Let the politicians fight over the definition of the algorithm, let them tweak it as much as they see fit. Just use the same algorithm for the entire nation and make its definition public. Would that process be political? Fuck yeah it would be! But it would be transparent and it wouldn't undermine faith in democracy. That is what is important here.

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Time Machines

FYI, I currently have an installation called Time Machines in a store window at 11th & Commerce in Tacoma. It will be there for another 6 weeks. And hopefully, now that I have a timer rebooting things every 4 hours, the triggering electronics should even be reliable!

(Oh, and yeah, I'm doing more in Tacoma over the next year, as I was chosen as one of the artists for this project.)

Pollice verso

So, you know that thing where a Roman emperor would decided if a gladiator should die by turning his thumb down or not? Turns out... maybe. All we actually know is that thumb turning (pollice verso) was involved. They might have been turned down. They might have been turned up, or hidden inside the fingers. I have my own theory.

Imagine the scene, the Colosseum at the height of imperial Roman power. A mighty gladiator stands in the bloody sand, his sword held against the throat of his fallen foe. Panting heavily, he looks up to the emperor. A hush falls across the audience as all turn to see the verdict. Slowly the emperor stands, looking sternly out across the masses who worship him as a living god. He raises his hand, holds out his thumb, drawing out the moment to make the most of his crowd-pleasing investment. Then, decisively, he sticks his thumb in his mouth and pulls it out with a loud *POP*. After a moment it is echoed by the other officials in his box. The sound quickly spreads in a crackling chorus through the stands, turning into raucous cheers as the sword is thrust home below.

That's got to be how it happened.

Improving protests

A problem I've been thinking over for many years is how to improve protests. It seems to me that the standard models are largely broken at this point, in that they don't motivate political change very well. If you read sources from the 60s, protests were scary back then. They were seen as a collapse of hierarchy, of basic social order. But we've developed cultural antibodies since then. We've learned to see the chaos of protests not as a threat, but as a humorous weakness. You've got the old hippies, you've got the same, tired old chants, you've got the people with the giant puppets, you've got hangers-on with signs for completely unrelated issues, you've got the wannabe anarchists breaking windows. All just a big, easily-ignored joke.

I've spent a lot of time trying to think of ways this could be fixed, how to break protests out of old ruts. There is a fine line to be walked: how do you convey power of the kind that politicians pay attention to, without it tipping over into bad kinds of power. The kinds that make you look like violent fascists, for instance. They used all the really obvious options, unfortunately.

The Occupy movement was interesting for this reason -- it was so weird and different, it managed to get a lot of attention at first. But camping doesn't convey power in the long run. It conveys homelessness, which is more or less the complete opposite in our society. So it fizzled. Maybe if they had standardized on some unique, homemade tent structures, like hexayurts? Getting people to make things to even a rough spec beforehand shows dedication and power. And hexayurts look so alien, it would have been very striking. And well insulated!

The pink "pussyhats" at the Women's Marches this weekend surprised me by being so effective. I admit I had dismissed the idea, in part because I didn't think they'd be so common. They provided strong visual cohesion, and they demonstrated many hours of effort beforehand. Being homemade clothing, they tied into some very deep American traditions of protest, providing a particularly nice contrast with mass-produced, foreign-made MAGA hats. They were uniform without being too uniform. They even worked to spread the protest out across the city after the march, as people made their way home. I was seeing them for the rest of the day around Seattle, providing a really interesting temporal echo to the protest.

Less well structured ideas follow:

I have long wondered about choreographed dance routines. Getting that many people to move in unity shows coordination and dedication, without necessarily being as bad-scary as marching in lockstep. It has the advantage of being able to dial in the exact amount of scariness, depending on how goofy the dance number is. But then I realized that this is exactly what the North Korean "Mass Games" are, and those actually trace back to Russian Revolution era practices. So, promising, but maybe not.

Brainstorming with someone (sorry, I forget who), we came up with the idea of radical construction as a protest activity. Imagine a swarm of people coming from every direction, each person carrying a custom, numbered strut. Working together in a way that could only come from practicing many times, they quickly erect a dome or tower. This could be in a park, or it could be in the middle of a busy intersection. Maybe they climb it and chain themselves to it, maybe not. But just the act of creation like that, showing literal coordinated industry, would be really striking in a new way.

Protest signs could use some innovation. How about a night march, protesters dressed in dark clothing, with signs lit up using LED strands and el-wire? 2017 is going hard cyberpunk, after all, so let's protest in style!

Who else has ideas? What is new/weird/different enough to break through cultural apathy, strongly visual, shows coordination and dedication and power, all without being the wrong kind of scary?


Like most people, I've commonly wondered how my life would have been different given various changes. What if we had moved when I was young, what if I had other siblings, etc. How would I be different? At what point would that alternate me be an unrecognizably different person? That's a fine course for a daydream to take, but a serious analysis raises unsettling questions.

First off, what does it mean to ask how things would have turned out in a counterfactual? Any basic understanding of chaos theory and quantum indeterminacy should quickly disabuse you of the idea that there would be a single possible result. The instant you create the new timeline, an uncountable number of fundamentally random differences start building on each other. Create the same new timeline, different results. None of them would be any more real or correct than the other. So, on this level, counterfactuals are a pretty meaningless concept. Even if you had access to them somehow, comparing the prime reality to any one possible alternate would be meaningless.

We have to give up the idea of a single alternate timeline. The question cannot be "what would have happened?" but "what is the distribution of results that would have happened?". It's meaningful to think about the range of results that could have been. Assuming access to the other timelines, you could build up an understanding in terms of mean outcomes. On average, what would my life have been like if X? (Or, if the distribution is multimodal, a more sophisticated analysis than simple mean, of course.) That would give something I could really compare myself to, the me I most likely would have been if X. That would be the most meaningful, most real alternate version of myself to think about.

Great! Except... I can turn those same tools onto myself. Just as there is a cloud of almost infinite different timelines around every historical change we could make, prime reality has the same cloud. By the arguments above, if we re-ran history from a given point, even not making any changes at all, we'd get different results. I'm surrounded by other possible versions of myself, even without the ability to make changes! And that set of mes has its own distribution, showing the most likely me. Which raises the question, how do I compare to that me? How likely am I? And if I find I'm not very likely, that I'm living far out on the tail somewhere, what does that mean? I was quite happy previously to define the maximum a posteriori estimation of myself in alternate histories as the most meaningful version. The most real. I might be very far from the most real version of myself. I might not be very like myself at all.

I'm not sure what to do with this realization.

Kids these days

1) There is a natural cognitive bias, the older one gets, to see society as going downhill.

2) I have been increasingly worried about social trends for several years now.

It's getting very hard to write off my worries as just being a symptom of #1. All the antisocial behavior we kept excusing as something "just on the internet" has been leaking more and more into the physical world. We all spend all our time in an environment where the only response to the most hideous of attacks is just "oh, ignore it, it's not serious". Of course empathy is becoming increasingly unfashionable! Even traffic is getting more aggressive, with people breaking the speed limit much more consistently and to greater average degrees it seems. But obviously it's hard to trust those observations.

Is there an intellectually rigorous method for resolving this dilemma?

Urbanist thoughts

This is a weird time to be a dedicated urbanist. Cities are popular again -- everyone is finally acknowledging what I always knew to be right! Real development is happening in them again, with a focus on walkable, liveable neighborhoods. That's great... except for how it is pushing out all the diversity which made the cities interesting in the first place. The new construction is all so bland and safe and boring, and every few days we lose another neat old building to it just here in Seattle alone. I know I will never have the cool shop I've always wanted, in some old brick industrial building. They're all condos already.

I don't see any way around it, unfortunately. We failed to invest in cities for the entire second half of the 20th century in this country, during which the population more than doubled. They have a huge technical debt which will take decades to pay off. Even if there was some way to stop it (if you know how to reliably, easily subvert market forces on this scale, please let me know!), it would just mean continuing to throw resources in the cultural, environmental, psychic pit that is the American suburb at the expense of cities. No thanks.

Eventually, hopefully, we'll get back to balanced cities which have enough housing for everyone, with strong transit systems that help the poor instead of gentrifying them out into the exurbs. The current overwhelming sameness of the new construction will fade as things age and get remodeled. We'll end up with a healthy blend of buildings in various states of disrepair, supporting a wide range of uses like Jane Jacobs talked about. For much of my life, cities were seen as mostly for poor people. Now suddenly they're only for rich people. But both of those are anomalous on the scale of human history. Cities used to be for everyone, and I see no reason they can't be once again.

But it does really kind of suck right now, and likely will continue to for at least the next 20 years.

ETA: This was partly inspired by reading Happy City, and partly as a reminder to myself to walk the walk. The University District in Seattle is about to be considerably upzoned, since the light rail station will be open in a few years and students don't form NIMBY coalitions. Which is great -- creating a second area of truly dense urban living in the city is huge. But it'll inevitably destroy the squalid charm of the Ave, which I unironically love. There is also a good chance it will push away two of my favorite retail establishments of all time, Hardwick's Hardware and Thai Tom's. I can't help but feel conflicted, so I need to focus on the big picture.